1 //! The "version 2" disk representation of the dirstate

     2 //!

     3 //! # File format

     4 //!

     5 //! The file starts with a fixed-sized header, whose layout is defined by the

     6 //! `Header` struct. Its `root` field contains the slice (offset and length) to

     7 //! the nodes representing the files and directories at the root of the

     8 //! repository. Each node is also fixed-size, defined by the `Node` struct.

     9 //! Nodes in turn contain slices to variable-size paths, and to their own child

    10 //! nodes (if any) for nested files and directories.

    11 

    12 use crate::dirstate::parsers::clear_ambiguous_mtime;

    13 use crate::dirstate::parsers::Timestamp;

    14 use crate::dirstate_tree::dirstate_map::{self, DirstateMap};

    15 use crate::dirstate_tree::path_with_basename::WithBasename;

    16 use crate::errors::HgError;

    17 use crate::utils::hg_path::HgPath;

    18 use crate::DirstateEntry;

    19 use crate::DirstateError;

    20 use crate::DirstateParents;

    21 use bytes_cast::unaligned::{I32Be, U32Be, U64Be};

    22 use bytes_cast::BytesCast;

    23 use std::borrow::Cow;

    24 use std::convert::{TryFrom, TryInto};

    25 

    30 

    31 #[derive(BytesCast)]

    32 #[repr(C)]

    33 struct Header {

    34     marker: [u8; V2_FORMAT_MARKER.len()],

    35 

    36     /// `dirstatemap.parents()` in `mercurial/dirstate.py` relies on this

    37     /// `parents` field being at this offset, immediately after `marker`.

    38     parents: DirstateParents,

    39 

    40     root: ChildNodes,

    41     nodes_with_entry_count: Size,

    42     nodes_with_copy_source_count: Size,

    43 }

    44 

    45 #[derive(BytesCast)]

    46 #[repr(C)]

    47 struct Node {

    48     full_path: PathSlice,

    49 

    50     /// In bytes from `self.full_path.start`

    51     base_name_start: Size,

    52 

    53     copy_source: OptPathSlice,

    54     entry: OptEntry,

    55     children: ChildNodes,

    56     tracked_descendants_count: Size,

    57 }

    58 

    59 /// Either nothing if `state == b'\0'`, or a dirstate entry like in the v1

    60 /// format

    61 #[derive(BytesCast)]

    62 #[repr(C)]

    63 struct OptEntry {

    64     state: u8,

    65     mode: I32Be,

    66     mtime: I32Be,

    67     size: I32Be,

    68 }

    69 

    70 /// Counted in bytes from the start of the file

    71 ///

    72 /// NOTE: If we decide to never support `.hg/dirstate` files larger than 4 GiB

    73 /// we could save space by using `U32Be` instead.

    74 type Offset = U64Be;

    75 

    76 /// Counted in number of items

    77 ///

    78 /// NOTE: not supporting directories with more than 4 billion direct children,

    79 /// or filenames more than 4 GiB.

    80 type Size = U32Be;

    81 

    82 /// Location of consecutive, fixed-size items.

    83 ///

    84 /// An item can be a single byte for paths, or a struct with

    85 /// `derive(BytesCast)`.

    86 #[derive(BytesCast, Copy, Clone)]

    87 #[repr(C)]

    88 struct Slice {

    89     start: Offset,

    90     len: Size,

    91 }

    92 

    93 /// A contiguous sequence of `len` times `Node`, representing the child nodes

    94 /// of either some other node or of the repository root.

    95 ///

    96 /// Always sorted by ascending `full_path`, to allow binary search.

    97 /// Since nodes with the same parent nodes also have the same parent path,

    98 /// only the `base_name`s need to be compared during binary search.

    99 type ChildNodes = Slice;

   100 

   101 /// A `HgPath` of `len` bytes

   102 type PathSlice = Slice;

   103 

   104 /// Either nothing if `start == 0`, or a `HgPath` of `len` bytes

   105 type OptPathSlice = Slice;

   106 

   107 /// Make sure that size-affecting changes are made knowingly

   108 fn _static_assert_size_of() {

   109     let _ = std::mem::transmute::<Header, [u8; 72]>;

   110     let _ = std::mem::transmute::<Node, [u8; 57]>;

   111 }

   112 

   113 pub(super) fn read<'on_disk>(

   114     on_disk: &'on_disk [u8],

   115 ) -> Result<(DirstateMap<'on_disk>, Option<DirstateParents>), DirstateError> {

   116     if on_disk.is_empty() {

   117         return Ok((DirstateMap::empty(on_disk), None));

   118     }

   119     let (header, _) = Header::from_bytes(on_disk)

   120         .map_err(|_| HgError::corrupted("truncated dirstate-v2"))?;

   121     let Header {

   122         marker,

   123         parents,

   124         root,

   125         nodes_with_entry_count,

   126         nodes_with_copy_source_count,

   127     } = header;

   128     if marker != V2_FORMAT_MARKER {

   129         return Err(HgError::corrupted("missing dirstated-v2 marker").into());

   130     }

   131     let dirstate_map = DirstateMap {

   132         on_disk,

   133         root: read_nodes(on_disk, *root)?,

   134         nodes_with_entry_count: nodes_with_entry_count.get(),

   135         nodes_with_copy_source_count: nodes_with_copy_source_count.get(),

   136     };

   137     let parents = Some(parents.clone());

   138     Ok((dirstate_map, parents))

   139 }

   140 

   141 impl Node {

   142     pub(super) fn path<'on_disk>(

   143         &self,

   144         on_disk: &'on_disk [u8],

   145     ) -> Result<dirstate_map::NodeKey<'on_disk>, HgError> {

   146         let full_path = read_hg_path(on_disk, self.full_path)?;

   147         let base_name_start = usize::try_from(self.base_name_start.get())

   148             // u32 -> usize, could only panic on a 16-bit CPU

   149             .expect("dirstate-v2 base_name_start out of bounds");

   150         if base_name_start < full_path.len() {

   151             Ok(WithBasename::from_raw_parts(full_path, base_name_start))

   152         } else {

   153             Err(HgError::corrupted(

   154                 "dirstate-v2 base_name_start out of bounds",

   155             ))

   156         }

   157     }

   158 

   159     pub(super) fn copy_source<'on_disk>(

   160         &self,

   161         on_disk: &'on_disk [u8],

   162     ) -> Result<Option<Cow<'on_disk, HgPath>>, HgError> {

   163         Ok(if self.copy_source.start.get() != 0 {

   164             Some(read_hg_path(on_disk, self.copy_source)?)

   165         } else {

   166             None

   167         })

   168     }

   169 

   170     pub(super) fn entry(&self) -> Result<Option<DirstateEntry>, HgError> {

   171         Ok(if self.entry.state != b'\0' {

   172             Some(DirstateEntry {

   173                 state: self.entry.state.try_into()?,

   174                 mode: self.entry.mode.get(),

   175                 mtime: self.entry.mtime.get(),

   176                 size: self.entry.size.get(),

   177             })

   178         } else {

   179             None

   180         })

   181     }

   182 

   183     pub(super) fn to_in_memory_node<'on_disk>(

   184         &self,

   185         on_disk: &'on_disk [u8],

   186     ) -> Result<dirstate_map::Node<'on_disk>, HgError> {

   187         Ok(dirstate_map::Node {

   188             children: read_nodes(on_disk, self.children)?,

   189             copy_source: self.copy_source(on_disk)?,

   190             entry: self.entry()?,

   191             tracked_descendants_count: self.tracked_descendants_count.get(),

   192         })

   193     }

   194 }

   195 

   196 fn read_nodes(

   197     on_disk: &[u8],

   198     slice: ChildNodes,

   199 ) -> Result<dirstate_map::ChildNodes, HgError> {

   200     read_slice::<Node>(on_disk, slice)?

   201         .iter()

   202         .map(|node| {

   203             Ok((node.path(on_disk)?, node.to_in_memory_node(on_disk)?))

   204         })

   205         .collect()

   206 }

   207 

   208 fn read_hg_path(on_disk: &[u8], slice: Slice) -> Result<Cow<HgPath>, HgError> {

   209     let bytes = read_slice::<u8>(on_disk, slice)?;

   210     Ok(Cow::Borrowed(HgPath::new(bytes)))

   211 }

   212 

   213 fn read_slice<T>(on_disk: &[u8], slice: Slice) -> Result<&[T], HgError>

   214 where

   215     T: BytesCast,

   216 {

   217     // Either `usize::MAX` would result in "out of bounds" error since a single

   218     // `&[u8]` cannot occupy the entire addess space.

   219     let start = usize::try_from(slice.start.get()).unwrap_or(std::usize::MAX);

   220     let len = usize::try_from(slice.len.get()).unwrap_or(std::usize::MAX);

   221     on_disk

   222         .get(start..)

   223         .and_then(|bytes| T::slice_from_bytes(bytes, len).ok())

   224         .map(|(slice, _rest)| slice)

   225         .ok_or_else(|| {

   226             HgError::corrupted("dirstate v2 slice is out of bounds")

   227         })

   228 }

   229 

   230 pub(super) fn write(

   231     dirstate_map: &mut DirstateMap,

   232     parents: DirstateParents,

   233     now: Timestamp,

   234 ) -> Result<Vec<u8>, DirstateError> {

   235     // TODO: how do we want to handle this in 2038?

   236     let now: i32 = now.0.try_into().expect("time overflow");

   237 

   238     let header_len = std::mem::size_of::<Header>();

   239 

   240     // This ignores the space for paths, and for nodes without an entry.

   241     // TODO: better estimate? Skip the `Vec` and write to a file directly?

   242     let size_guess = header_len

   243         + std::mem::size_of::<Node>()

   244             * dirstate_map.nodes_with_entry_count as usize;

   245     let mut out = Vec::with_capacity(size_guess);

   246 

   247     // Keep space for the header. We’ll fill it out at the end when we know the

   248     // actual offset for the root nodes.

   249     out.resize(header_len, 0_u8);

   250 

   251     let root = write_nodes(&mut dirstate_map.root, now, &mut out)?;

   252 

   253     let header = Header {

   254         marker: *V2_FORMAT_MARKER,

   255         parents: parents,

   256         root,

   257         nodes_with_entry_count: dirstate_map.nodes_with_entry_count.into(),

   258         nodes_with_copy_source_count: dirstate_map

   259             .nodes_with_copy_source_count

   260             .into(),

   261     };

   262     out[..header_len].copy_from_slice(header.as_bytes());

   263     Ok(out)

   264 }

   265 

   266 /// Serialize the dirstate to the `v2` format after clearing ambigous `mtime`s.

   267 fn write_nodes(

   268     nodes: &mut dirstate_map::ChildNodes,

   269     now: i32,

   270     out: &mut Vec<u8>,

   271 ) -> Result<ChildNodes, DirstateError> {

   272     // `dirstate_map::ChildNodes` is a `HashMap` with undefined iteration

   273     // order. Sort to enable binary search in the written file.

   274     let nodes = dirstate_map::Node::sorted(nodes);

   275 

   276     // First accumulate serialized nodes in a `Vec`

   277     let mut on_disk_nodes = Vec::with_capacity(nodes.len());

   278     for (full_path, node) in nodes {

   279         on_disk_nodes.push(Node {

   280             children: write_nodes(&mut node.children, now, out)?,

   281             tracked_descendants_count: node.tracked_descendants_count.into(),

   282             full_path: write_slice::<u8>(

   283                 full_path.full_path().as_bytes(),

   284                 out,

   285             ),

   286             base_name_start: u32::try_from(full_path.base_name_start())

   287                 // Could only panic for paths over 4 GiB

   288                 .expect("dirstate-v2 offset overflow")

   289                 .into(),

   290             copy_source: if let Some(source) = &node.copy_source {

   291                 write_slice::<u8>(source.as_bytes(), out)

   292             } else {

   293                 Slice {

   294                     start: 0.into(),

   295                     len: 0.into(),

   296                 }

   297             },

   298             entry: if let Some(entry) = &mut node.entry {

   299                 clear_ambiguous_mtime(entry, now);

   300                 OptEntry {

   301                     state: entry.state.into(),

   302                     mode: entry.mode.into(),

   303                     mtime: entry.mtime.into(),

   304                     size: entry.size.into(),

   305                 }

   306             } else {

   307                 OptEntry {

   308                     state: b'\0',

   309                     mode: 0.into(),

   310                     mtime: 0.into(),

   311                     size: 0.into(),

   312                 }

   313             },

   314         })

   315     }

   316     // … so we can write them contiguously

   317     Ok(write_slice::<Node>(&on_disk_nodes, out))

   318 }

   319 

   320 fn write_slice<T>(slice: &[T], out: &mut Vec<u8>) -> Slice

   321 where

   322     T: BytesCast,

   323 {

   324     let start = u64::try_from(out.len())

   325         // Could only panic on a 128-bit CPU with a dirstate over 16 EiB

   326         .expect("dirstate-v2 offset overflow")

   327         .into();

   328     let len = u32::try_from(slice.len())

   329         // Could only panic for paths over 4 GiB or nodes with over 4 billions

   330         // child nodes

   331         .expect("dirstate-v2 offset overflow")

   332         .into();

   333     out.extend(slice.as_bytes());

   334     Slice { start, len }

   335 }